Worlds of Magic: Planar Conquest (UP)

This one can be a little confusing. In order to build a new city, you will first need a unit that can do this. This is the first unit in the list underneath your training menu, such as a Pioneer or Settler. So the first step is to train one of these units.

Once the unit is ready you need to move to an available spot to build. You must be at least 5 tiles from another city and the spot must allow you to build there. This is where it is kind of confusing because the only way you know is by moving the unit around on the game tiles and keep pressing to check if the Build City is available at the top of the action wheel. The option will simply be missing if you cannot build (versus it just being grayed out). Keep moving across world tiles until the option is available.

Once it is available, use it and the trophy will immediately unlock.